


the perks of unity

by corsica



Category: Fate/Grand Order
Genre: Double Penetration, Established Relationship, F/M, Plot What Plot/Porn Without Plot, Polyamory, Threesome - F/M/M, fuck outta here with that, there is no incest in this fic, why did i even bother tagging characters when i did all that bullshit w/ the relationship tags
Language: English
Status: Completed
Published: 2021-03-19
Updated: 2021-03-19
Packaged: 2021-03-28 15:22:03
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 4,933
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/30141594
Author URL: https://archiveofourown.org/users/corsica/pseuds/corsica
Summary: When they want to work together, they work together well.
Relationships: Arjuna | Archer/Female Fujimaru Ritsuka, Arjuna | Archer/Fujimaru Ritsuka, Arjuna | Archer/Fujimaru Ritsuka/Karna | Lancer of Red, Female Fujimaru Ritsuka/Karna | Lancer, Fujimaru Ritsuka/Karna | Lancer of Red
Comments: 6
Kudos: 14





	the perks of unity

**Author's Note:**

> i rolled arjuna on his rate up during the chaldea boys collection on only 6 summon tickets so i felt morally and legally obligated to write this gratuitous shlock lest karma punish me for my hubris. i hope you guys like semicolons.
> 
> thank you for coming home my sweet boy even though you are utterly outclassed by gilgamesh in every way. time to put you and your brother in family counseling. 
> 
> now _pspspspspsps come home as a berserker on the yuga kshetra banner pspspspspsps_

* * *

She does not pair them together much for combat.

It's more for practical reasons than anything else; there are other Archers that have better synergy with Karna, and there are other Lancers that have better synergy with Arjuna. Ritsuka is used to maneuvering around old wounds and bad blood between Servants if she needs them to cooperate for something, so their past has never been an issue. It's just happenstance that there's been little reason to put them together for anything.

But if it happens—

If they want to—

They can work together seamlessly.

_“Ah—.”_

Arjuna is a cool presence behind her, already shed to just his purple shirt and white pants. He removes her hair tie and tosses it out of the way before he tilts her head back and up to bring her lips to his, impatience dripping from every movement before he sighs in relief against her mouth. His hands are just as temperate as the rest of his body, his fingers strong and his touch as hard or soft as it needs to be. He kisses her insistently, teeth biting and lips sucking, doing his best to coax out as many noises from her as he can. Ritsuka moans his name and his lips quirk up into a smile against hers.

Sliding his hand down, he brings his other one up to deftly unhook the harness around her chest and he lets it fall to the ground. The pouches around her hips are next, and as Arjuna loosens that, Karna has finally untied her boots enough to slip them and her socks off.

Karna stands just in time for the pouches around her waist to unceremoniously fall and join the harness on the floor. The kiss breaks with Arjuna, but Karna is quick to take over, gentle fingers turning her head towards him so he can firmly slot his mouth over hers. He exudes _so_ much heat; the roaring fire to Arjuna's storming rain, and he kisses her slowly, thoroughly, as if every second is precious, draws his name out from her throat in a whimper. Ritsuka can see the steam he exhales when they momentarily part, and as she gasps in air, his eyes meet hers, and they are just as heated as the rest of him.

His hand leaves her face to push down her jacket and he gets it off of her enough that Arjuna can tug it down by the sleeves. The piece of clothing is haphazardly discarded to the side; Arjuna does not care where it lands, because her neck is now exposed, and he eagerly puts his lips to the pale expanse. As Karna kisses her, swelling her lips and winding their tongues together, Arjuna pulls aside the sleeve of her tank top to sink his teeth into the junction between her neck and shoulder; she whines into the kiss, and Karna shudders.

“I—.” Karna breaks the kiss, cheeks tinted red, and he leans down to kiss her neck, which gives Arjuna the opportunity to take over once more; she has been and is being kissed so breathlessly, and her thoughts are so fuzzy from the pleasure, that the only word she's able to get out between Arjuna's lips taking hers over and over again is, “Bed.”

They glance at each other for a moment, and then Ritsuka is caught between two pairs of hands. As Karna pushes, Arjuna pulls, and their mouths press against any and every inch of her skin available to them.

She's hauled up onto the bed with an “oof”, legs dangling off the edge. Arjuna climbs up, behind her once more, while Karna looms over her, standing at the foot of the bed. His fingers dip beneath the hem of Ritsuka's tank top as he kisses her, lips searing hers, gone hotter than they already were. The kiss breaks long enough for Arjuna to finish yanking her top off, mouth covering hers once she's down to her bra, and he tempers the residual heat that Karna left behind as his teeth graze against her lips.

Karna sinks to his knees; his fingers curl around her foot, holding it delicately in his hand as his lips brush against the top in reverence. His hands slide up her calves, up her thighs, up, up, up until they are under the waistbands of her skirt and underwear. He pulls them down at the same time, tosses them in the general direction of her other removed clothes, and gently pushes her knees apart so he can settle between her legs. The skin of her inner thighs is tender; Karna takes great pains to be careful, to not bite too hard as he nips little marks into her.

The embarrassment she feels from the sheer amount of sincerity Karna puts in every single action towards her is cut short by Arjuna's hands kneading her breasts through her thin, lacy bra. His thumbs draw circles around and around her until she is hard and peaked, and she's forced to bite down on her lower lip to muffle the loud whine that he pulls from her as his thumbs roll back and forth. She's still moaning when he lets go of her, and she's thankful for the respite…but then she realizes just how short-lived it's going to be as he unhooks the clasp on her bra. He noses lovingly at her temple, and kisses near the top of her head. Her face flushes; Arjuna's quiet laughter vibrates through his chest, as he is undoubtedly able to see just how red her ears have become. With one last, deep breath, Ritsuka gathers her courage and weakly lifts her arms, letting Arjuna slip off the last bit of clothing she's wearing.

“There's no need to be embarrassed,” Arjuna murmurs against her skin, and he's _right—_ they've done this more times than any of them can count, but the shyness is impossible to break out of in spite of how hard she tries, and it's only made _worse_ when he reaches for her hands, slots his fingers between the spaces of hers, and says, so earnestly, “You're beautiful, Ritsuka.”

Karna leans forward, kisses against her quivering stomach, “She's always beautiful,” he pulls back, lifts her legs up onto his shoulders, “…But she looks best like this.”

The flush on her face brightens like a lamp when he says that, only growing stronger as she feels Karna run a finger against her. She is so, so slick, and Karna's eyes are unmoving on her. When he sees just how much drips out of her, his breath comes out in a long, haggard exhale, and then he spreads her apart with his thumbs. Ritsuka's pulse picks up. Arjuna's hands break from her own, settle on her waist before they slide up to cup her chest once more, and her pulse rushes even faster.

It almost becomes too much, but before more embarrassment can settle in, Karna puts his mouth against her and Arjuna pinches her between his fingers and she _melts._

Ritsuka breathes out an airy little _'oh'_ and is quick to snap her hand down and sink it into Karna's hair, urging him on, something he needed no encouragement for—something he will _never_ need encouragement for. He spreads her wider, runs his tongue against her in long, flat strokes, drawing out soft moans and softer whimpers. Ritsuka's other hand grips the sheets of her bed tightly, fabric twisting and bunching up between the spaces of her fingers.

Where Karna is methodical, Arjuna is _relentless;_ his lips suck mark after mark in her neck, working her full breasts over with firm, insatiable fingers, pinching and tugging until she is bright red and pebbled beneath his fingertips, where just a graze is enough to make her whine in need. He breathes hard against her skin, whispers words in his native language that she recognizes as things he's said before, sweet nothings he'd reluctantly translated for her later with a sheepish look on his face.

Arjuna grinds against her, straining beneath his pants and craving friction. Her hand comes off her sheets, fingers trembling, and she fumbles with the clasp of his pants. Ritsuka hears him chuckle against her ear, but it turns into a groan when he is finally hard and thick in her palm.

A genuine attempt is made to properly touch him, to try and do for him what he's doing for her, but Karna moves up, takes her between his lips and sucks, and as he curls his tongue around her there isn't much more she can do other than dig her hand further into his messy white hair and breathlessly gasp _'more, more, please'_ in-between keening moans. Arjuna seems to mind little, if at all, bucking up into the tight circle formed by her hand around him.

He kisses against Ritsuka's temple affectionately, and his low, muttering voice reverberates through his body and into Ritsuka's, “Don't hold back, Master.”

They are always quick to work her up, and Ritsuka knows she won't last long—she never does, and they'll make sure she never will. Her thighs tremble around Karna's head, his tongue striking her over and over again, but he lets her slip out from between his lips, catching and tasting the slick that spills out of her as his tongue licks up in a slow drag. Arjuna nips at the helix of her ear, gently flicks his thumbs against her. Her breathing has been reduced to desperate, rapid panting, and whenever she tries to speak, the only thing that comes out is the airy sound of one of their names.

And oh, how hard they try to get her to say _their_ name. Cooperative, maybe, but they're just as competitive as always.

A soft cry of _'Karna…'_ has Arjuna crushing their mouths together to silence her, biting her lower lip just a bit too harshly, pinching her between his fingers with a punishing intent, and a gasp of _'Arjuna…'_ has Karna briefly pulling away to leave imprints of his own teeth all over her inner thighs, and when she starts to say Arjuna's name again, her voice cuts off with a strangled moan as Karna's tongue prods inside of her with a bit more force than strictly necessary.

Her body grows taut, and she's close, perilously so, and they know it, and at the same time Karna has her in his mouth, gently, _gently_ grazing his teeth against her, Arjuna's thumbs roughly roll over her breasts, and Ritsuka arches her back, letting out a shuddering moan that wracks her body before she goes completely tense. Both of them pause for a moment, eyes wide and caught off-guard by just how strong her reaction is.

…And then they do it again.

Arjuna's hands move as she peaks, one coaxing her to let go of his length so he can take her own hand, help her ride it out, and she squeezes his fingers tightly. His other hand settles on her hip as his arm wraps around her waist, leaving slow kisses against her neck as her small, whining moans begin to die down.

Karna gradually pulls back from between her legs, breathes out a light cloud of steam. He licks the tips of his thumbs, swipes his tongue over his lips, and wipes his mouth on the back of his hand. When he takes Ritsuka's own limp hand off the top of his head, he is quick to link their fingers together before he stands up and places one knee on the bed. Arjuna keeps Ritsuka held against him as he scoots back to give him room.

With his free hand, Karna cups the side of Ritsuka's face, stroking at the heavy flush that colors her cheeks and ears; her eyes open after a few moments, fiery orange now glazed-over and glassy—shining in the light like beautiful, amber gemstones. He leans in, touches their lips together in a slow, soft kiss as Arjuna moves her so she's on her knees. Ritsuka feels the hum of the words _'I love you'_ spoken against her, and she weakly returns the squeeze that Karna gives to her hand.

Arjuna kisses up her shoulder, and tilts her face towards his when Karna pulls back and takes his hand away from her cheek. The kiss is short and sweet, and the way her head is turned gives Karna the chance to mark along unclaimed spots on her neck.

“Is it still under your pillow?” Arjuna asks. Ritsuka gives a small nod, and her hand separates from his as he briefly leaves her. She startles, lets out a cry that is both surprised and wanting for more as Karna kisses down, places his mouth around her breast, laving against it with his tongue; he cups the other with his hand and circles around her with his thumb. When he pulls away—earning a displeased whine from Ritsuka—he hums thoughtfully.

“That's a poor place for it,” he says, matter-of-fact, “Someone else will find it eventually.”

“Karna, I honestly”—he leans down to kiss her, interrupting her, and Ritsuka playfully nips on his bottom lip before he breaks away—“have more important things to be thinking about right now.”

“Yes,” Arjuna murmurs low against her ear, pressed right against her back again, and Ritsuka shivers as she feels his slicked fingers press against her ass, “You do.”

The initial push is always strange, always so foreign, and she tenses up with a whimper. Arjuna peppers kisses along her neck, and without a word, Karna's own hand glides down, fingers parting her folds, and his eyes go slightly wide, because she has only become even _more_ drenched since he had his mouth on her. The next breath that comes out of him is hard, a little shaky. He squeezes her hand, and pushes a finger inside of her; there is no resistance, and she is so warm and _tight_ around him.

His fingers are long, longer than Arjuna's, and slender, and once he's deep inside of her, he curls in and strokes, making her shiver and gasp uncontrollably. That helps ease her tension; Arjuna slowly begins to move his own finger now that it isn't causing her as much discomfort. Whenever she begins to tense again, Karna covers her mouth with his and catches the moans she lets out as he rubs inside her.

Ritsuka squeezes Karna's hand one last time before she lets go. She draws aimlessly around the red gem in his chest before her hand goes down, touching the last bit of armor he still hasn't taken off. Her finger moves back and forth, back and forth against the edge where it meets his blackened skin, and the silent request is (finally) met. Gold gives way to another patch of white skin amid the black, and his breath hitches against her lips as she takes him in her hand, stroking from base to tip.

“It's only fair I touch you, too…” she murmurs. Karna breathes out a short, quiet laugh.

“I'm not interested in fair play,” he touches his forehead to hers, “I'd rather make you feel good.”

He pushes another finger into her at the same time Arjuna does, and Ritsuka whines, hopelessly caught between the two of them. She tries to put her hand back on Karna, but he catches it, links her fingers with hers. Trying to touch Arjuna yields the same result, and all she can do is become the panting, writhing mess they're making of her.

“But I want to— _nn…”_ her words are cut off as Karna winds his tongue around hers; he licks his lips when he pulls back, dives down to her neck, and her head turns instinctively towards Arjuna to give Karna more room. Arjuna happily takes advantage, and Ritsuka moans faintly as he kisses her. His fingers twist and scissor inside of her, working in deeper and deeper, and the initial foreign feeling has finally morphed into that pleasurable fullness.

“You're getting close again, aren't you?” he asks, voice gentle, and Ritsuka makes a noise of confirmation; Arjuna takes her lips in his, and though he keeps it brief, he makes the most of it, panting when he pulls back, “I thought so.”

Karna kisses her again as Arjuna sucks at her pulse. He slows in his movements, and Ritsuka can sense hesitation coming from him. She's two seconds away from asking if there's something wrong, but that thought is ripped out of her as he carefully adds a third finger inside of her. There are no words in her mind as he pumps his fingers in and out; all she can do is let out a weak cry and clamp down around him. Karna exhales in a shudder, kisses against her shoulder and lets his eyes fall shut as he feels her trembling grow stronger and stronger. Ritsuka spreads her legs wider, rocking back and forth, trying to pull both of them further inside her body. The moan Arjuna lets out is muffled as he kisses her, overwhelmed by how she _aches_ for them.

He murmurs words she can't understand against her ear again when the kiss breaks, but Arjuna catches himself, chuckles with his next breath, and kisses the side of her head.

“I love you,” his voice is barely loud enough for her to hear. Ritsuka turns her head enough so that he can touch her forehead to his, and the look she sees in his eyes only confirms what he said even more.

With one last, tender kiss to her lips, Arjuna moves down her neck, leaving a trail of red marks in his wake. His teeth sink in to the junction between her neck and shoulder, and he shoves both of his fingers into her to the last knuckle the same time Karna does.

Karna's lips press against her temple as Arjuna's press against the base of her neck, and her hands are held tightly as she shudders between them again, weak little moans freely pouring out of her as her back bends into a deep arch. Their fingers stay inside of her as she rides through the aftershock, moving with intent, trying to milk every last drop from her. Wetness trickles down Karna's hand and coats her inner thighs, and Ritsuka sobs, jerking back and forth against them.

“T-Too much, it's…” Ritsuka chokes out a gasp, clings to their hands in desperation, “Pl—ease, I _can't—.”_

They finally cease, and she tumbles forward against Karna, her forehead resting against his collarbone. He slides his fingers out first, and she whines at the lost feeling. Arjuna is next, and he lets go of her hand as well, fingers curling around her waist as he kisses down the exposed skin of her back.

“Beautiful…”

Karna finishes licking the last of her off his fingers, and Ritsuka starts to rustle against him. She looks up at him with an expression nothing short of needy, eyes half-lidded, dark and sensual. Her skin is flushed scarlet and damp with sweat, littered with red marks and teeth indents claiming her all over her neck, shoulders, chest and thighs. Arjuna presses his lips slowly to the bruising marks he'd left on her back, almost apologetically, before dipping his head down to make new ones where he could.

Pure black fingers come up to brush her bangs out of her eyes. Ritsuka keeps her glassy stare on Karna as he does so. When he brings his hand back, Ritsuka tugs her own free, and he is briefly confused, grunting in surprise as she grabs his face and pulls him down, shoving her tongue in his mouth. The kiss is sloppy, but that doesn't make it any less satisfying, and Karna matches her with graceless motions of his own.

A thin line of saliva connects them when Ritsuka breaks off, gulping down air, “I want…more…”

“Oh?” Arjuna smiles against her skin, and he moves, kissing up her spine to her shoulder as his fingers slide up to cup her breasts again, and her back arches with a needy whimper as he flicks his fingertips against her, “But you're so oversensitive… Will you be able to handle it?”

“Mm…” she nods, and Arjuna scrapes his teeth against the side of her neck, “I still feel like I might be able to walk tomorrow…” her head turns, looks at Arjuna, before her eyes dart over to Karna, “Can't have that, can we?”

“I would be disappointed in myself if I didn't leave you fully satisfied,” Arjuna says, and his hands slide down, right arm wrapping around her waist, left hand raising her left leg, “How disgraceful…calling myself a Servant when I am unable to serve you properly. I won't allow that.”

Karna cups the side of her face, looking at her lovingly, “Are you sure you'll be alri—?” as Karna runs his thumb over her lips, they part, and Ritsuka takes his finger into her mouth; a fire lights up his eyes, tender blue gaining an acute hunger, and they close entirely as he takes a deep breath, left hand trailing down to lift up her right leg, “…I guess that answers my question.”

He slips his thumb out of her mouth, replaces it with his lips. Ritsuka cups his face with one hand, trails her fingers down with the other, tracing against the lines of lithe muscle on his body, before she takes him in her hand and guides him inside of her. She swallows down the hitch in his breath, and she feels cool liquid behind her again as she takes Karna to the hilt with a pleased sigh. The kiss with him breaks, and Arjuna nudges her face towards his, tongue pushing and twisting around hers as he ruts against her. Ritsuka reaches behind herself, takes him between her fingers and gasps into his mouth as he slowly pushes inside of her. His brow furrows, and he buries her face in her neck, squeezing her once he is all the way in.

“…So tight,” Arjuna's voice is muffled against her neck, and his fingers uncurl from around her waist as Ritsuka reaches for his right hand, “Yet each time you take me, it's as if you can't get enough.”

“Insatiable, aren't you?” Karna murmurs in-between kisses against her neck.

 _“Yes,”_ the word comes out in a single, hot breath.

Ritsuka firmly holds onto Arjuna's hand as she grabs for Karna's, and Arjuna chuckles at her response, “Your honesty is appreciated, Master,” he kisses against the back of her neck, “Even if you're only telling us things we already know.”

Karna links his fingers with hers, “Are you ready?”

Ritsuka nods, feels both of them kiss the hands they're holding, and then they start to move.

She is pinned between them, head full of pleasure and fog, and in very little time their rhythm becomes steady, slow but synchronized. Their names come out of her in half-formed moans; the irritation from one of them when she starts to say the name of the other is like a blanket of lead on her, but it's not long before she's unable to say anything at all besides the word _'please'_ wrapped around quiet _'oh'_ s. Both of them are all over her; it feels like they press their mouths _everywhere,_ and though she is able to tell who is kissing her at the start—Karna is always so _warm,_ always kissing her like he will never be able to do it again, and Arjuna is always so _temperate,_ always kissing her like he never wants to stop—but soon enough both are breathing hard, their bodies hot and their lips possessive, and it's impossible for her to tell who is stopping and who is starting.

All she can do is moan and whine and _beg_ with a yearning desperation into the mouth of whoever is kissing her, bucking back and forth because _it's not enough._

 _“Please—.”_ Ritsuka's voice comes out as a needy mewl, and she's just barely able to flutter her eyes open when one of them pulls back from a kiss—Arjuna, and his deep brown eyes have gone even darker. That wicked little smirk plays at his lips, and the next words out of his mouth are said every other breath.

“Still not enough for you?” he squeezes her hand, sucks against the pulse point right under her ear, “How greedy…”

“Insatiable,” Karna repeats himself in one ragged breath before he scrapes his teeth against her neck.

Ritsuka grinds her hips down as best she can, needing to pull them deeper, wanting more and more and _more,_ but she's stopped as they both move in against her. There's no space between their bodies on either side of Ritsuka, leaving her with even more limited movement than she already had as they control the pace entirely. What had started slow is now raw and _primal;_ Arjuna pants against her ear, pulling out nearly all the way before he roughly bucks back into her, dragging out a noisy cry from Ritsuka that dies down into a series of whimpers as he nips at her ear. Karna matches his ferocity with ease, biting down on her shoulder as he rocks his hips sharply against her—long, smooth thrusts becoming much more forceful while still being just as precise, while staying just as harmonious.

Tears form at the corners of her eyes, her body hypersensitive and overstimulated. Her voice is almost entirely gone, no longer able to moan, only able to gasp desperately for air against the lips of whoever is kissing her as they rut into her.

“Soon, soon,” she rasps out, _“Please please please please…”_

They are not far behind, from what she can tell, if how hard they're gripping her hands is any indication. Her body grows taut, tenses up, and the few tears in the corners of her eyes spill down her cheeks in small beads as they kiss and bite and suck against every sensitive spot she can think of on her neck, back, chest, and shoulders. She is _so_ close, both of them driving into her with rapid, plunging thrusts, and she's shaking like a leaf from her head to her curled toes.

“I can't…”

Karna kisses up to her left ear, and he says her name in a harsh exhale.

“Ritsuka.”

Arjuna's breath is warm against her right ear as he speaks her name in a sigh.

“Ritsuka…”

They tighten the grip they have on the hands they hold, giving her the same demand, at the same time:

_“Say my name.”_

She doesn't.

What she does instead is lose what's left of her voice in a cracked, broken cry, a tremor surging through her body as she finally reaches climax. Her body seizes, and distantly, she hears swearing, and they both shudder and grunt as they spill inside of her; she doesn't know who was first, and frankly isn't all that concerned with it.

They both remove themselves from her before they let go of the respective leg they are holding up, and Ritsuka falls back in a boneless heap against Arjuna as she catches her breath. She feels their spend beginning to seep out of her, and she wrinkles her nose, because it's a feeling she'll never quite get used to. Ritsuka attempts to move her legs, but it's a lost cause, and any words she tries to say come out in a croak. Knowing that this was going to happen doesn't make it any less exasperating.

Arjuna moves first, being the only one of the three who has clothes that need to be straightened out. He lets out a sigh as his pants are finally buttoned back up, and soon after there is a gleam of light as Karna's armor comes back on. Ritsuka's eyes open hazily; Arjuna has his arm wrapped around her midsection, and he lets his lips linger in a kiss against the back of her hand. Karna is doing the same thing, but pulls back when he notices her staring. He smiles at her, and though it starts off gentle and loving, she watches as his expression shifts to looking a _bit_ too proud of himself for being able to reduce her to this state.

…Arjuna finishes kissing her hand, buries his face against her neck, and she can feel _his_ self-satisfied little smirk, too.

Before she can tell them to stop acting so damn _pleased_ with themselves like they do _every_ time they do this, they move, and so does she; they maneuver her in tandem until she is laying on her back in the middle of her bed. Arjuna lays on her right side, Karna on her left, and they are both reaching for one of her hands once more.

She closes her eyes, smiles to herself.

_'I guess I'm supposed to rest, now.'_

It's not the worst idea in the world, and maybe she'll have her voice back when she wakes up. So Ritsuka feels Arjuna kiss the top of her head, feels Karna kiss against her cheek, and she lets herself fall to the sweet void of sleep.

Right before she succumbs, she hears the words _“I love you”_ from two distinct voices, and her lips quirk up into one last smile before she sleeps. It's something she hears every time, seconds before she's unconscious, and it's always so cute, that they think she can't hear them.

If only they were this cooperative all the time.

**Author's Note:**

> i know the chaldea beds probably aren't big enough for three people but they're both twinks so its fine.


End file.
